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Radon zones in Maryland

The EPA assigns every county in Maryland to one of three radon potential zones. 8 are in Zone 1, the highest category, home to about 52% of the state's residents.

24
Counties
8
Zone 1 counties
Predicted average above 4 pCi/L
9
Zone 2 counties
Predicted average 2-4 pCi/L
7
Zone 3 counties
Predicted average below 2 pCi/L

The map

Radon potential across Maryland

Every county in Maryland, filled by the zone the EPA assigns it. Zones follow geology rather than county lines, so the colour usually changes where the bedrock does, not where the border is.

Zone 1 · 8Zone 2 · 9Zone 3 · 7

Hover a county · click to open it

County by county

All 24 Maryland counties

Zone 1 · > 4 pCi/LZone 2 · 2 - 4 pCi/LZone 3 · < 2 pCi/L
CountyZonePopulationCOPDSmokingLung ca. deaths
Baltimore County1845k6.5%11.1%33.8
Calvert County195k5.9%11.1%39.7
Carroll County1177k5.9%10.9%35.2
Frederick County1293k5.1%9.2%25.8
Harford County1265k6.1%10.9%34.8
Howard County1336k4.0%7.4%19.5
Montgomery County11.1M4.5%7.2%16.8
Washington County1156k8.4%15.1%36.0
Allegany County267k9.7%17.7%35.9
Anne Arundel County2595k5.2%10.6%31.4
Baltimore city2565k7.3%15.8%42.9
Cecil County2106k7.7%15.3%45.0
Charles County2172k5.5%11.5%33.6
Garrett County228k9.3%14.2%25.6
Prince George's County2947k5.5%10.5%21.5
Somerset County225k8.7%16.9%44.7
St. Mary's County2115k5.9%12.7%34.4
Caroline County334k9.5%17.4%49.8
Dorchester County333k9.9%16.1%37.9
Kent County319k8.1%11.9%31.5
Queen Anne's County353k6.8%11.7%25.8
Talbot County338k8.0%10.9%31.7
Wicomico County3105k7.4%13.4%44.9
Worcester County354k8.0%12.3%32.1

Zones from the EPA Map of Radon Zones. COPD and smoking are CDC PLACES model-based estimates of adult prevalence. Lung cancer death rates are age-adjusted deaths per 100,000 per year, 2019-2023, from NCI State Cancer Profiles. A dash means the source does not report a value for that county.

Highest potential

Zone 1 counties in Maryland

These 8 counties have a predicted average indoor radon screening level above the EPA action level. The EPA recommends every home in them be tested.

Other states

Radon zones elsewhere